An Italian physicist and astronomer. In introducing the use of the telescope into astronomy he brought about a revolution in the observation of celestial bodies. He discovered in particular the relief of the Moon, the rotation of the Sun around its axis, Jupiter’s main satellites, the phases of Venus and the presence of stars in the Milky Way. Won over to Copernicus’ heliocentric theory (the Earth is not the centre of the Universe; it gravitates around the Sun), Galileo was brought before the Inquisition’s tribunal, which condemned him and forced him to retract, on his knees (1633). Just after this retraction, he is nevertheless supposed to have exclaimed: ‘Eppur’, si muove!’ ‘And yet it moves!’ (the Earth). The Church finally rehabilitated him...in 1992. Galileo was also one of the precursors of modern mechanics and played a major role in the introduction of mathematics to explain the laws of physics. He also gave a preliminary formulation of the principle of relativity.